Diversity:

Orcs are an incredibly diverse group, consisting of 6 distinct species: Goblins, Gremlins, Hobgoblins, Gorkens, Ridgelings and Ogres. The Ogres are diversified further, consisting of seven distinct sub-species. One would think that such diversity would breed intolerance. But Orcs are bond together by a deeply rooted social philosophy called "The Three Green Rules" (see below).

The Three Green Rules:

Long ago Ogre and Goblin societies were highly unorganized, with neither having a centralized government. Ogres, at that time, were little more then roving bands of primitive beasts. And Goblins were divided into countless small tribes that bickered constantly. Both races suffered terribly for this lack of organization. The combination of infighting and the encroachment of humans and other races nearly drove Ogres and Goblins to extinction. After Elf invaders attacked and destroyed an Ogre settlement called "Ork City" - an unusually large Ogre by the name of "Davisi" and an unusually intelligent Goblin by the name of "Gob'Onary" joined forces to fight the invaders. They achieved a small measure of success that gained them both a lot of fame. Using the ruins of Ork City as a base of operations Davisi and Gob'Onary formed a new tribe of both Goblins and Ogres. They also established a set of laws called the "Three Green Rules" which they insisted that ALL Goblins and Ogres MUST obey. This became the foundation of what would become the Orc Empire.

The three green rules are as follows:
1) Green creatures that weald weapons are sacred allies. 
2) Green creatures that weald weapons shall be known as "Orcs" or "Greenskins".
3) All other forms of life are merely cattle, beasts, prey, tools, mounts, slaves, food or targets.

As the Empire grew, more "green creatures that weald weapons" were discovered and adopted by the Empire. Today there are 6 races of Greenskins: Ogres, Goblins, Hobgoblins, Ridgelings, Gremlins and Gorkens.

There have been two periods in Orc history where the three green rules were called into question. The first was called the "Great Gorken Debate" and the second was called the "Great Fungusloth Debate".

Great Gorken Debate:

The Three Green Rules were adopted long before Orcs had discovered Gorkens. So at one time Gorkens were not considered "Orcs" because they could not, and still can't, weald weapons. But most Orcs very much wanted Gorkens to be included. This sparked the "great Gorkens debate". The Ogres, Hobgoblins and Goblins have a soft spot for Gorkens. For them a Gorken is a domestic pet, tank, trusted friend, jeep, and war buddy all in one. Most Orcs found the classification of Gorken as "non-Orc" to be very disturbing. After all, "non-Orc" is just about the worst thing a life form can be. So great was the desire to make Gorkens official members of "Orc-kind", that the following rationalization was created:

"When Gorkens allow armed Greenskins to ride them into battle - they are 'wielding the riders'. And since the riders weald weapons - the Gorkens also wield weapons. Therefore they are Orcs."

This extremely contrived rational was gladly accepted, and is now considered an unquestionable fact, by Orc society.

The Great Fungusloth debate:

Not long after Gorkens officially became members of Orc-kind, creatures called "Fungusloths" were discovered. Fungusloths are undeniably green and they frequently weald weapons. In fact Fungusloths are almost never seen without a crude weapon of some sort. But they are loathed by Orcs for the following reasons:
1) Their bodies produce tiny spores that goblins and hobgoblins are violently allergic to.
2) They are incredibly stupid; Their ability to wield crude weapons appears to be derived, not from intelligence, but from highly evolved instinct.)
3) They have no concept of war; there actions are motivated only by their instinctive desire to reproduce and eat.
4) Fungusloths infest and destroy crops.
5) They are also very very very smelly.

This created an obvious problem for Orcs. Clearly another rationalization was needed. It panned-out as follows:

"An object is only a weapon if it is used to wage war. Fungusloths do not wage war. Therefore the objects they wield are not weapons. Therefore they are not Orcs."

Rumbles:

Ogres prefer to fight non-Orcs, but will gladly fight with each other when there is no alternative. Such Ogre vs Ogre battles are called "rumbles".  Taking place on mutually decided battle grounds, "rumbles" are precisely scheduled and well organized - not unlike human sporting events. (Trolls are the only race of non-Orc to take part in these "rumbles" on a regular basis. Goblins and Hobgoblins, only take part a few times a year. Ridgelings only participate once a year during the Orc's annual "Chariot Crash" festival in New Ork City - were the grand prize for winning is a chest of silver.)

Money:

The first form of Orc currency was, of all things, salt. All living things, including Orcs, need salt to survive. At that time salt was rare and could only be obtained by mining. Even taxes were paid for in salt. For convenience the Orc parliament minted crude copper coins called "Forexs" that could be used to pay taxes instead of salt. The value of forex copper coins became tethered to the value of salt. Soon both forex coins AND salt became standard currencies in the Orc kingdom. 

The Orc economy took a terrible hit, however, when a simple means for manufacturing salt, from sea water, was discovered. The value of salt plummeted taking the value of the forex copper coins down with it. This created runaway inflation and forced the Orc economy to revert to an inefficient barter system.

In a rare display of creative competence - the Orc parliament mandated that taxes be paid in "Ogre Pearls" (also called Afterbirth Pearls*).

*(When a female Ogre gives birth, one of the byproducts that her body produces are "Afterbirth Pearls" or "Ogre Pearls". Typically there is one for each baby Ogre that is born. Ogre Pearls are small egg-shaped stones approximately 1/2 of an inch in length. They are very smooth, hard and unusually heavy for there size. They are yellow by firelight, but turn orange when exposed to the sun. There is no known way to artificially create Ogre Pearls.)
 
At the same time that parliament mandated that taxes be paid in Ogre Pearls, they also declared that they would give one Ogre Pearl in exchange for 1,000 forex copper coins. The mandate worked and forex copper coins once again had value. Ogre Pearls are typically used for large purchases such as land or cattle while Forex Copper Coins are used to pay for smaller purchases such as food or tools.

Besides Forex Copper Coins and Ogre Pearls - there are several "unofficial" currencies that Orcs sometimes use. They include such things as silver, gold and Cruzella tickets. The latter being the first recorded instance of paper currency being used by Orcs. In Non-Orc societies, gold is worth ten times as much as silver. But in Orc society silver has almost the same value as gold. This is mostly due to the special dietary needs of Ridgelings. (See "Ridgelings")